They do have a trackpad, but not in this shape.

I was surprised when I started using the Steamdeck. The Steamdeck's trackpad felt almost identical to my trackball mouse, and it took effectively no time to get used to it.

The advantage of a trackball over a trackpad is that you can spin the ball for high movement speed, then stop it after a set time for fairly accurate distance. A trackball (or trackpad) will never be as accurate as a regular moue, but it is surprisingly usable (after a few months or practice).

The mouse stays in one location with grippy feet and the trackball moves the cursor. There is no sensor for mouse movement. It does take a while to get used to.

The reason I chose it was that I didn't have enough desk space to move a mouse. I barely even had enough space to put the mouse. Now that I've moved house, I just like the novelty. It's not as accurate as a regular mouse.

I would love a mouse that could do both regular movement and trackball movement so I could have 4 axis inputs. Sadly, I haven't found any like that.

I helped a user who exclusively uses a trackball and started getting used to it within seconds. My thumb was definitely not used to the trackball but I very quickly adapted and could navigate the computer normally

Overuse and poor lighting.

I know some people have used an acetone vapor bath with ABS prints. I've never looked into what works with PLA.